I wish to change the tax amount in checkout programmatically I am using following code let me know If I am making any mistake.
$session= Mage::getSingleton("checkout/session");
$quote_id = $session->getQuoteId();
$quote = Mage::getModel("sales/quote")->load($quote_id);
$items = $quote->getAllItems();
foreach($items as $item) {
$item->setTaxAmount(0);
$item->setBaseTaxAmount(0);
$item->setPriceInclTax($value);
$item->setBasePriceInclTax($value);
$item->save();
$quote->save();
}